1. Field of the Invention
The present invention relates to a multilayer ceramic chip capacitor enabling an improvement in the specific dielectric constant and a reduction in the dielectric loss and superior in capacity-temperature characteristic even when the dielectric layers are thin and a method for production of the same.
2. Description of the Related Art
Extensive use is being made of multilayer ceramic chip capacitors as electronic devices due to their small size, large capacity, and high reliability. Large numbers are also used in single electronic apparatuses. In recent years, along with the increasingly smaller size and high performance of apparatuses, there have been stronger demands for further reduction of the size, increase of the capacity, and improvement of the reliability of multilayer ceramic chip capacitors.
A multilayer ceramic chip capacitor is ordinarily produced by stacking an internal electrode paste and dielectric paste by the sheet method, printing method, etc. and cofiring them. In general, Pd or a Pd alloy is used for the electroconductive material for the internal electrodes. Pd is high in cost, so relatively inexpensive Ni or Ni alloys or other base metals are now being used. When using a base metal as the electroconductive material of the internal electrodes, if firing in the atmosphere, the internal electrode layers end up oxidizing, so it is necessary to cofire the dielectric layers and the internal electrode layers in a reducing atmosphere. If firing in a reducing atmosphere, however, the dielectric layers are reduced and the specific resistance ends up becoming lower. Therefore, nonreducing dielectric materials are being developed.
To reduce the size and/or increase the capacity of a multilayer ceramic chip capacitor, it is necessary to make the layers of the dielectric thinner and/or increase the number of layers. Further, it is necessary to use a dielectric with a high dielectric constant. At the present time, layers are being reduced in thickness to give less than 3 xcexcM between layers. If the dielectric layers are made thinner, however, the electric field acting on the dielectric layers becomes strong when applying voltage, so the dielectric loss becomes remarkably greater and the capacity-temperature characteristic also ends up deteriorating.
On the other hand, to prepare a dielectric with a high dielectric constant, there is the method of increasing the crystal grain size of the dielectric layers such as by increasing the grain size of the ingredient powder forming the main component of the dielectric layers.
As nonreducing dielectric magnetic compositions enabling a reduction in thickness to less than 3 xcexcm, there are for example the barium titanate type disclosed for example in Japanese Unexamined Patent Publication (Kokai) No. 9-241074 and Japanese Unexamined Patent Publication (Kokai) No. 9-241075. These however have a dielectric constant of 1000 to 2500 or so. Ones with a high dielectric constant become too large in dielectric loss.
An object of the present invention is to provide a multilayer ceramic chip capacitor enabling an improvement in the specific dielectric constant and a reduction in the dielectric loss and superior in capacity-temperature characteristic even when the dielectric layers are thin and a method for production of the same.
To achieve the above object, there is provided a method of production of a multilayer ceramic chip capacitor having a capacitor body configured by alternately stacked dielectric layers and internal electrode layers, comprising using as a powder ingredient of barium titanate for forming the dielectric layers a powder ingredient having a ratio (I(200)/Ib) of a peak intensity (I(200)) of a diffraction line of a (200) plane with respect to an intensity (Ib) at an intermediate point between an angle of a peak point of a diffraction line of a (002) plane and an angle of a peak point of a diffraction line of a (200) plane in an X-ray diffraction chart of 4 to 16. Preferably, the ratio (I(200)/Ib) is 5 to 15.
Preferably, the powder ingredient of barium titanate has mixed in it a first subcomponent ingredient forming silicon oxide (first subcomponent) after firing.
The molar ratio of the first subcomponent to 100 moles of the main component BaTiO3, when calculating the molar ratio by converting the barium titanate included in the dielectric layers after firing to BaTiO3 and the silicon oxide to SiO2, is preferably not less than 2 moles and not more than 12 moles, more preferably not less than 2 moles and not more than 6 moles.
The powder ingredient of the barium titanate preferably has mixed in it a second subcomponent ingredient forming an R oxide (where R is at least one type of element selected from Sc, Y, Eu, Dy, Ho, Er, Tm, Yb, and Lu; second subcomponent) after firing.
The molar ratio of the second subcomponent to 100 moles of the main component BaTiO3, when calculating the molar ratio by converting the barium titanate included in the dielectric layers after firing to BaTiO3 and the R oxide to R2O3, is preferably from 0 to not more than 5 moles, more preferably not less than 0.1 mole and not more than 3 moles.
The powder ingredient of the barium titanate preferably has mixed in it a third subcomponent ingredient forming at least one of magnesium oxide, zinc oxide, and chromium oxide (third subcomponent) after firing.
The molar ratio of the third subcomponent to 100 moles of the main component BaTiO3, when calculating the molar ratio by converting the barium titanate included in the dielectric layers after firing to BaTiO3, the magnesium oxide to MgO, the zinc oxide to ZnO and the chromium oxide to xc2xd(Cr2O3), is preferably from 0 to not more than 3 moles, more preferably from 0 to not more than 2.5 moles.
The powder ingredient of the barium titanate preferably has mixed in it a fourth subcomponent ingredient forming manganese oxide (fourth subcomponent) after firing.
The molar ratio of the fourth subcomponent to 100 moles of the main component BaTiO3, when calculating the molar ratio by converting the barium titanate included in the dielectric layers after firing to BaTiO3 and the manganese oxide to MnO, is preferably from 0 to not more than 1 mole, more preferably from 0 to not more than 0.5 mole.
The powder ingredient of the barium titanate preferably has mixed in it a fifth subcomponent ingredient forming at least one of barium oxide, calcium oxide, and strontium oxide (fifth subcomponent) after firing.
The molar ratio of the fifth subcomponent to 100 moles of the main component BaTiO3, when calculating the molar ratio by converting the barium titanate included in the dielectric layers after firing to BaTiO3, the barium oxide to BaO, the calcium oxide to CaO and strontium oxide to SrO, is preferably from 0 to not more than 12 moles, more preferably not less than 2 moles and not more than 6 moles.
The powder ingredient of the barium titanate preferably has mixed in it a sixth subcomponent ingredient forming vanadium oxide (sixth subcomponent) after firing.
The molar ratio of the sixth subcomponent to 100 moles of the main component BaTiO3, when calculating the molar ratio by converting the barium titanate included in the dielectric layers after firing to BaTiO3 and the vanadium oxide to V2O5, is preferably from 0 to not more than 0.5 mole, more preferably from 0 to not more than 0.2 mole.
The specific surface area of the powder ingredient of the barium titanate is preferably 1.0 to 8.0 m2/g, more preferably 1.0 to 4.0 m2/g.
If the ratio (I(200)/Ib) of the peak intensity of the diffraction line is less than the above range, the dielectric loss of the obtained capacitor becomes larger. Preparation of samples with a ratio (I(200)/Ib) of peak intensity of the diffraction line over the above range is difficult.
If the specific surface area is less than the above range, the grain size of the ingredient powder becomes large and the IR accelerated lifetime tends to become poor when the layer is made thin. Further, preparation of samples with a specific surface area over the above range is difficult.
If the content of the first subcomponent is less than the above range, the sinterability will deteriorate. If the content is over the above range, the permittivity tends to fall. If the content of the second subcomponent is over the above range, the permittivity tends to fall and the sinterability to deteriorate. If the content of the third subcomponent is over the above range, the permittivity tends to fall and the capacity-temperature characteristic to deteriorate. If the content of the fourth subcomponent exceeds the above range, the permittivity tends to fall and the capacity-temperature characteristic to deteriorate. If the content of the fifth subcomponent exceeds the above range, the sinterability tends to deteriorate. If the content of the sixth subcomponent exceeds the above range, the permittivity tends to remarkably fall.
By controlling the characteristics in X-ray diffraction of the barium titanate ingredient powder comprising the dielectric layers to within the range of the present invention, it is possible to provide a large capacity multilayer ceramic chip capacitor having a high permittivity, a small dielectric loss, and a superior capacity-temperature characteristic.